Lithium house battery with a Honda BF150

Honda is a trademark of its owner. Amp Hour Supply isn’t affiliated with Honda.

Short answer: The BF150 puts out 40 amps of battery charging (55 amps total, per Honda). Honda also says its outboards were built around lead-acid batteries. So leave the start battery as Honda specs it, and feed a lithium house bank through a DC-DC charger that takes no more than 30 of those 40 amps.

The BF150’s numbers

What Honda’s figure Source
Charging output (BF150A) 12 V, 40 A Owner’s manual, specifications
Alternator, total 55 A, of which 40 A is battery charging Honda Marine BF115-140-150 page
Minimum start battery 12 V, 64 Ah (5-hour rate), 80 Ah (20-hour rate), 622 CCA Owner’s manual, battery
Alternator circuit fuse 100 A (ACG fuse) Owner’s manual, fuses
Battery type it was designed around Lead-acid, including AGM and gel Honda lithium-ion statement OTR55062

The 40 is what’s left for your batteries after the engine feeds itself. That’s the number to plan with.

Can a Honda BF150 charge a lithium battery?

Yes, with care, and Honda spells out the conditions. Its lithium statement says any lithium battery has to meet the engine’s amp-hour and CCA needs, have a battery management system that can shut it off, and be charged only by a charger made for lithium, inside the battery maker’s limits. Honda then sends you to the battery maker for the rest.

The simple way to meet all of that is to not touch the start side. Keep the start battery at Honda’s minimum or better, in the type Honda designed for. Put the lithium bank on its own, charged by a Victron Orion-Tr Smart 12/12-30 isolated DC-DC. The charger has a lithium profile you set to your battery maker’s numbers, and it caps its output at 30 A.

Why the cap matters here: 30 A is three quarters of the BF150’s 40 A. Victron’s manual also warns that an alternator at idle can give about half its rating. At trolling speed with the plotter, pumps and lights on, the motor may not keep up, and the Orion will stop with “engine shutdown detected.” That’s the charger protecting your start battery, not a fault. Run a bit more throttle, or cut a few loads, and it picks back up.

How the three charging options compare (plain combiner, lithium combiner, DC-DC) is in Charging lithium from a boat alternator: 3 ways compared. This page sticks to the Honda side.

You’ll need

Steps

  1. Check the start battery first. It should meet 64 Ah (5-hour rate) and 622 CCA at minimum. If it doesn’t, fix that before adding anything.
  2. Plan short runs. Honda warns that lengthening the original battery cable drops voltage at the engine. Leave Honda’s start cable alone. Take the charger’s feed from the start battery side with its own fused cable, and mount the charger near the house bank.
  3. Power down before you wire. Engine off, key out. Honda says pulling battery cables with the engine running damages the outboard’s electrical system. Never do it.
  4. Fuse the charger input at the start battery end with the 60 A fuse.
  5. Wire the output to the house bank, fused at the house battery.
  6. Set the charge profile in VictronConnect to your lithium maker’s voltages.
  7. Fit the SmartShunt on the house negative so you can see real amps going in at idle and at cruise.
  8. Test on the water. Watch the shunt at idle, then at cruise. If charging stops often at idle, you’ve found your boat’s limit.

If the engine ever stops charging altogether, Honda’s manual points to the 100 A ACG fuse. Check it before blaming the new gear.

Does this page fit your boat?

This page fits if you have a BF150A covered by Honda’s 2021 owner’s manual (US and Canadian models, serials BANJ or BAPJ 1400001 and later), one engine, and a 12 V house bank.

It doesn’t fit if you have an older BF150 outside that serial range, twin engines, a 24 V house system, or you want to replace the start battery itself with lithium. For an older motor, check your own manual’s charging figure. For a lithium start battery, Honda’s statement says to work it out with the battery maker.

Shore power or anything on the AC side is a job for a licensed marine electrician.

Products for this setup

Product Why it’s here
Victron Orion-Tr Smart 12/12-30 isolated DC-DC Takes at most 30 A of the BF150’s 40 A and charges with a lithium profile.
Victron SmartShunt 500A Shows what the motor actually delivers at idle and at cruise.
Victron Smart BatteryProtect 100A Cuts house loads before the bank runs too low. Loads only, not charging.

Prices show live from the store.

Bundles for this job: Dual-battery DC-DC charging kit, Boat lithium upgrade kit, large

Quick answers

How many amps does a Honda BF150 charge at? Honda rates the BF150A at 40 A of battery charging, out of 55 A total.

Does Honda allow lithium batteries? Honda says its outboards were designed for lead-acid, AGM and gel batteries. A lithium battery has to meet the engine’s Ah and CCA needs, have a BMS with shutoff and use a lithium charger, and Honda tells you to check with the battery maker.

Why won’t my DC-DC charger keep running at idle? At idle the motor gives less than its rated 40 A, and the charger stops when the start side sags. Higher rpm or fewer loads usually fixes it.

Sources

  • Honda BF115D/BF135A/BF150A Owner’s Manual 31ZX1626 (2021): https://cdn.powerequipment.honda.com/marine/pdf/manuals/00X31ZX16260.pdf
  • Honda Marine BF115-140-150 motor page: https://marine.honda.com/outboards/motor-detail/BF115-140-150
  • Honda Marine Lithium-Ion Battery Usage statement OTR55062 (Dec 2021): http://cdn.powerequipment.honda.com/marine/pdf/misc/120821_OTR55062_Marine Li-Ion Battery Statement.pdf
  • Honda Marine BF150 manuals page: https://marine.honda.com/support/manuals/models/BF150
  • Victron Orion-Tr Smart DC-DC Charger Isolated manual (Rev 14, 02/2026): https://www.victronenergy.com/upload/documents/Orion-Tr_Smart_DC-DC_Charger_-_Isolated/34439-Orion-Tr_Smart_DC-DC_Charger-pdf-en.pdf
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