Lithium starting power that won't kill your alternator.
Every drop-in lithium battery protects itself by disconnecting. On an inboard, that disconnect is exactly what destroys the charging system. WakeTender is engineered from the battery management up so the alternator always has somewhere to send its energy.
- Charge path isolates. Load path stays live. The alternator keeps a load at the one moment it matters.
- 30 lb. Less than half the weight of the AGM it replaces.
- Warns before it acts. Pre-disconnect alarm over CAN and Bluetooth.
- Rated for 110 A alternators. Published on the datasheet, not buried in a footnote.
The disconnect is the failure.
The internet argues about lithium overheating alternators. For a start battery that story is mostly wrong. A crank pulls a few amp-hours and the battery lives at full charge. The real damage happens in a few milliseconds, when a battery management system decides to open the circuit while the alternator is still producing.
The transient a disconnect throws at your electronics
Aftermarket alternator protection modules are built to clamp 60 V load-dump spikes, and designers have measured transients far higher. Rectifiers, ECUs and stereo amps were never specified for that.
Drop-in lithium start batteries that handle it inside the case
The industry's answer is a line on the spec sheet capping your alternator size, and a separate protection box sold as an accessory. The battery itself still just opens the circuit.
Battery whose failure strands the boat
A house bank that disconnects turns the lights off. A start battery that disconnects stops the engine, with the ballast full and the sun going down. It deserves a different design.
Built to stay connected.
We did not start with cells and a case. We started with the alternator, the engine harness and the moment a battery decides to protect itself, then engineered the battery to behave the way a boat needs it to.
When WakeTender stops accepting charge, it does not drop the bus.
Charging and discharging are handled on separate paths. If the pack ever needs to refuse charge, the charge path closes while the load path keeps conducting. Your alternator still sees the boat's electrical system. Your engine still sees its battery. No spike, no stall, no stranded crew.
Warns before it acts
An early warning fires over CAN and Bluetooth well before any charge disconnect, with time for a regulator, a charger or the helm to respond. ABYC E-13 recommends a pre-disconnect alarm. Almost no drop-in on the market has one. WakeTender does.
Rated for your alternator
Maximum alternator output: 110 A per battery, printed on the datasheet. Stock Indmar, PCM and Ilmor alternators sit comfortably under it. If you have a high-output upgrade, we will tell you straight instead of letting you find out on the water.
Cranks cold
Discharge is rated to −4 °F, so the first start of a cold morning on the lake happens. Low-temperature charge protection and internal heating look after the cells while you warm up.
30 pounds. Sealed to IP67.
Less than half the weight of the AGM it replaces, with a tray and strap in the box. Sealed to IP67, so a flooded bilge is an inconvenience rather than an event.
Certified, not just claimed
Cells and pack carry the listings a marine installer and an insurer actually ask about. The certifications are on the label, and the test reports are available on request.
Talks to the boat
State of charge, temperature, voltage and alarms over CAN for the builder and over Bluetooth for the owner. The battery stops being the one component on the boat with nothing to say.
WakeTender 120.
A 12.8 V, 120 Ah lithium iron phosphate battery, sealed to IP67, with a cell heater, a Bluetooth app and a CAN port built in, and a battery management system configured to be safe at the one position that matters most: the start battery. Run one at the start position, up to four in parallel as the house bank. Five-year warranty.
warranty
On the case
- Built-in cell heater. Warms the cells for low-temperature charging so a cold morning does not cost you a charge cycle.
- On/off isolation button. Isolates the terminals for storage, transport or service without pulling a cable.
- Reset button. Restarts the battery management system if it has protected itself, without tools.
- LED state of charge. Four-step charge indicator on the case, readable from the engine hatch.
- M8 terminals. One positive, one negative, torqued to 8–10 N·m. Standard marine lugs fit.
- M12 communications port. CAN and RS-485 for the builder's helm display or engine controller.
- Bluetooth app. Voltage, current, state of charge, temperature and alarms on iOS and Android.
What makes it a start battery
- Charge and load are controlled separately. If the pack refuses charge, only the charge path closes. The engine and the alternator keep their connection to the battery.
- It warns before it protects. An over-voltage warning is issued on CAN and Bluetooth with margin before any protective action, which is what ABYC E-13 asks for and almost no drop-in provides.
- Cranking passes straight through. Over-current protection is timed for sustained faults, not for the one-second event of a start. Only a hard short circuit trips instantly.
- A published alternator ceiling. 110 A per battery, on the datasheet. Stock Indmar, PCM and Ilmor alternators sit under it. High-output upgrades do not, and we say so.
- Cold-rated both ways. Charge and discharge are rated to −20 °C, with the heater covering the charge side.
| WakeTender 120 · preliminary specification | |
|---|---|
| Chemistry | Lithium iron phosphate (LiFePO4) |
| Nominal | 12.8 V · 120 Ah · 1,536 Wh |
| Dimensions | 12.2 × 8.4 × 6.7 in (309 × 213 × 170 mm) |
| Weight | 30 lb (13.6 kg) |
| Max continuous discharge | 150 A at 25 °C |
| Peak discharge | 500 A for 3 s |
| Max charge current | 100 A (60 A nominal) |
| Max alternator output | 110 A per battery |
| Expansion | Up to 4 in parallel (480 Ah) · up to 4 in series |
| Charge voltage | 14.2 – 14.6 V · float 13.5 – 13.6 V |
| Operating temperature | Charge and discharge −20 to 60 °C (−4 to 140 °F) |
| Cell heater | Built in, for low-temperature charging |
| Terminals | M8 × 1 positive, × 1 negative · 8–10 N·m |
| Controls | On/off isolation button · reset button · LED state of charge |
| Communications | Bluetooth app (iOS / Android) · CAN / RS-485 via M12 port |
| Ingress | IP67 (1 m, 30 min) |
| Certifications | UL 1973 · IEC 62619 · IEC 62133 · UN38.3 · CE |
| Cycle life | 6,000 cycles at 80% depth of discharge (deep-cycle rating) |
| Warranty | 5 years |
| In the box | Battery, tray and strap |
| Cranking data | Published on completion of testing |
One battery. Every position.
Boat builders do not want two chemistries on one boat, and they are right. WakeTender is the same battery at the start position and in the house bank: one at the engine, up to four in parallel behind everything else. Same cells, same protection, same app, and enough energy to stop rationing comfort.
The boat already has all of this. The bank hasn't kept up.
A 2027 flagship ships with a fridge-freezer, an espresso machine, 2,000 watts of household power, a vacuum-flush head, heated seats, four cameras, a stern thruster, six subwoofers and an app that reads battery voltage from your driveway. It runs them on roughly the same lead-acid bank a boat had twenty years ago. Every comfort gets negotiated against the last one. A 480 Ah usable bank ends the negotiation.
A full afternoon at anchor
Stereo, fridge, lights and the head for hours with the engine off. Four batteries give you more than twice the usable energy of four AGMs, and lithium holds its voltage until the end, so the last hour sounds like the first.
Real household power
A 2,000 W inverter at full output pulls about 170 A from a 12 V bank. That is above one battery's continuous rating and well inside a bank of four. Espresso, a blender or a charger for the foil does not dim the lights.
Always on, never dead
Telematics, keyless ignition and the app draw a little, all the time. Two weeks on the lift drains an AGM bank. On a lithium house bank it is a rounding error, and the battery reports its own state of charge over the same link.
Lead-acid gives up about half its label before you start shortening its life. Lithium iron phosphate gives up nearly all of it. Usable capacity is the number that decides how long the stereo plays at anchor.
Usable capacity, four in parallel
Roughly two and a half times the usable energy of four Group 31 AGMs, in the same number of trays.
Lighter than four AGMs
120 lb instead of about 260 lb, which is weight you can put back into ballast.
Chemistry on the boat
Same battery at the start position and in the house bank. One charge profile, one app, no mixed-chemistry rules.
The part we will put in writing.
Engine manufacturers prohibit lithium start batteries on charging-system grounds, and they are right to: the batteries they have been shown deserve it. This is an engineering objection, so here is an engineering answer.
What actually fails
Three failure modes get blamed on lithium. Alternator overheating from low internal resistance is real for a house bank being bulk-charged from 50 percent, and nearly irrelevant for a start battery that lives at full charge and gives up one to three amp-hours per crank. That is why a WakeTender house bank charges from shore power and a DC-DC charger, never straight off the engine's alternator. Overcharge from a fixed 14.2 to 14.7 V regulator is a non-event for lithium iron phosphate.
The third mode is the one that strands boats. A battery management system opens the circuit while the alternator is producing. The field energy has nowhere to go and the bus spikes. Rebuilders see the result as blown rectifiers. Owners see it as a boat that stopped. The industry's response has been to cap alternator size on the datasheet and sell a separate clamp module. Neither changes what the battery does at the moment of disconnect.
What WakeTender does at that moment
Charge acceptance and load delivery are controlled independently. An over-voltage event closes the charge path only. The load path keeps conducting, so the alternator retains the boat's electrical system as a sink and the engine retains its battery. Before any of that happens, a warning is issued on the CAN bus and to the app, with enough margin for a regulator or ECU to intervene. That satisfies the pre-disconnect alarm ABYC E-13 (13.7.4) recommends, which most drop-ins ignore.
Over-current protection is set so that a cranking event passes through untouched: the thresholds and delays are long compared with a start, and the only fast-acting protection is the hard short-circuit trip. Charge-side current limiting defines the published 110 A alternator ceiling.
What we will not say
We are not printing a cold cranking amp number we have not measured. Marine lithium "CCA" ratings currently come in four incompatible flavors, none of them verified by a third party. WakeTender cranking data comes from instrumented testing with a current probe on a scope, not a clamp meter that misses a 150 ms inrush, and it will be published when testing is complete.
| Behaviour | Conventional drop-in | WakeTender |
|---|---|---|
| On over-voltage | Opens the whole circuit | Charge path closes, load path stays live |
| Before disconnecting | No warning | CAN + Bluetooth alarm with margin |
| Alternator limit | Footnote, if stated | 110 A per battery, on the datasheet |
| ABYC E-13 13.7.4 alarm | Not met | Met |
| Cranking rating | Unverified "CCA" | Scope-measured, published |
| Engine integration | None | CAN telemetry and alarms |
If your lithium prohibition is written around charging-system compatibility, we would like to put a unit on your bench and let your instruments decide. Tell us what would have to be true for you to approve a lithium start battery, and we will build to that.
The questions behind the questions.
Plain-English engineering for owners, dealers and the people who have to sign off.
Straight answers.
The questions owners, dealers and engineers ask first, answered the way we would answer them in person.
Can a lithium battery be used as the starting battery on an inboard wake boat?
Lithium iron phosphate cranks a marine V8 without difficulty. Cranking was never the problem. The problem is what a lithium battery does when its management system decides to stop accepting charge while the alternator is still producing. WakeTender is engineered around that moment: the charge path closes, the load path stays connected, and a warning goes out before anything happens.
Will a lithium start battery damage my alternator?
A conventional drop-in can. When its battery management system opens the whole circuit with the alternator running, the alternator's field energy has nowhere to go and the bus voltage spikes. That transient, called a load dump, is what takes out rectifiers and electronics. WakeTender never opens the load path, so the alternator always has somewhere to send its energy, and it issues a warning over CAN and Bluetooth before it refuses charge.
Do engine manufacturers approve lithium starting batteries?
Most inboard engine manufacturers currently specify lead-acid or AGM starting batteries and cite charging-system compatibility as the reason. That is an engineering objection, and WakeTender is built to answer it. We are seeking evaluation by boat builders and engine manufacturers. Until an approval exists, check your engine warranty terms before changing battery chemistry.
What size alternator can I run with WakeTender?
Up to 110 A per battery. Stock alternators on Indmar, PCM and Ilmor inboards are typically 95 A, which sits comfortably under the limit. A high-output alternator upgrade above 110 A is not supported on a single battery.
How many WakeTender batteries can I run on one boat?
One at the start position, and one to four in parallel as the house bank, for up to 480 Ah. The house bank connects to the engine side through an ACR or DC-DC charger and charges from shore power, so the engine's charging circuit serves the start battery only. Up to four can also be wired in series for 24 or 48 V systems.
Will it fit my battery tray?
WakeTender 120 measures 12.2 × 8.4 × 6.7 inches (309 × 213 × 170 mm) and weighs 30 lb. It is not a BCI Group 31 case, so measure your tray. A tray and strap are included.
Will it start the boat in the cold?
Discharge is rated to −20 °C (−4 °F), so it cranks on a cold morning. A built-in cell heater handles charging below freezing. Cranking data from instrumented testing publishes when testing is complete.
What is the warranty?
Five years.
What does WakeTender cost and when can I buy one?
WakeTender is in development. Pricing is published with the first production units. Email sales@waketender.com to be told first.
What is ABYC E-13?
E-13 is the American Boat and Yacht Council standard for lithium-ion batteries on boats. It recommends that a battery warn the operator before its management system disconnects. Most drop-in lithium batteries do not. WakeTender does, over CAN and Bluetooth.
Talk to the people building it.
WakeTender is in development. If you own a wake boat, sell or service them, or build the boats and engines that go in them, we would like to hear what you are seeing with batteries and charging systems, and what you would need from a lithium start battery before you would trust one.