I recently bought a 2005 boat with an onboard charger for both batteries. I changed the trolling motor battery to a lithium and don't think the onboard charger is fully charging the lithium. I have a stand alone lithium charger that I can probably mount somewhere. I don't have $ for another charger, what do I do? My thought was putting a plug strip and attaching both chargers and running the plug out.

a 2005 charger probably isn't lithium compatible (they charge to a set voltage of around 14.4V for lithium but 13.4 or so for lead). If that's the case and you already have a lithium compatible charger, it looks like you need to run two chargers. Make sure the onboard is disconnected from the lithium battery and just connect it each time. It's a pain, but it if works then fine. You can maybe change out the terminal connections on the lithium charger so that it is easier for you each time. The Noco Genius for instance have removable battery end leads where you could put ring ends on it and then leave the end portion on the battery. Then just plug the end of the charger into that when you get home.

I'm gonna say that a 2005 onboard charger definitely is NOT compatible. Modern lithium battery technology didn't even begin until about 2010.

If you do purchase another onboard charger at some point, make sure it specifically states that it can be used with a lithium battery. Some cannot.

The strip idea is the part I’d skip. Older onboard chargers are usually the wrong charge profile for lithium, so I’d keep the onboard charger on the lead-acid battery and use the standalone charger for the lithium battery, even if that means a separate plug-in routine. If you want to make it easier, leave a quick-connect pigtail on the lithium charger so you are not fighting battery terminals every time. Do you already have a plug-in lead on that charger, or is it bare ring terminals?

Alex from GA If I understand your original post a nd when you say strip you're describing a 120v power distribution strip. You'll plug the extension cord into the strip and then plug in each charger separately. If so, that should work well.

Be sure you tape off the un-used bank to prevent a short circuit. You don't describe your lithium charger, is it designed for LiFePO4 lithiums? If not, you should consider replacing it with a Noco Genius 10 single bank charger that has the correct profile for a LiFePO4 battery. They're under $100 bucks.

I added a lithium house battery to my boat. My on board charger couldn't handle another battery so I bought a lithium compatable charger. I wired a plug to the lithium battery so I can quickly plug in the charger for it. I use one of these on the end of my extension cord and plug the onboard charger into one outlet and the lithium charger (which is not installed on the boat) in the other.

If the lithium charger is connected to the battery but unplugged does it discharge the battery?

6 hours ago, Alex from GA said:

If the lithium charger is connected to the battery but unplugged does it discharge the battery?

From experience, yes but at a very slow rate.

On 4/18/2026 at 9:35 AM, Alex from GA said:

If the lithium charger is connected to the battery but unplugged does it discharge the battery?

I lost 3% on my 100AH TM lithiums over the winter (late November through early March) per the bluetooth app. So I'd guesstimate 1% discharge per month.