testing battery?
 

Got battery for my trolling motor (100ah marine deep cycle)

Should get 3 hours run time on full charge. Ain't happening.

First 2 times I had it out, my cheapo ampmeter from amazon said it was 100% charged at rest and 90% under load when first launching, and was reasonable accurate based on run time vs. percent left claimed.

Last few trips out, with no load ampmeter is showing 85% after being on charge for 48 hours, and under load it immediately drops to 55%, which again seems to be accurate. Yesterday had it out, and when it was reporting 0% I was still moving but at about half max speed. Fortunately only a few hundred yards from boat ramp, and we returned under power with no paddling. But it was close.

So... I am about to go back to the FLAPS where I bought the thing, have them test it, and possibly get a new one (yay 1 year warranties). Should I charge it as much as I can first, or take it to them in its current "mostly dead" state?

I have no idea on the appropriate test for a deep cycle battery. But make sure that you charge it up before taking it back. If it's not fully charged, they are likely to tell you "we can't check it until it's charged."

Yeah, I'll charge it for 48 hours and take it in. I'm hoping they just replace it or give me store credit to get a replacement (would really like LiFePo for the weight savings)

I used a deep cycle battery in a race car w/o an alternator/generator in the '70's. The retailer said not to use a regular auto battery charger on it. Can't remember why though.

I recently bought a couple of 100ah LiFepo4 deep cycles for my electric outboard which produces 55 lb.s of thrust. After running wide open for 3 hours the battery is still strong and feels fresh. So much better than the old lead batteries. A third of the weight, comes with it's own smart charger which has its own port next to the 2 USB plugs. Game changer for under $200 on Amazon.

I have a car battery that I am 99% sure is bad. When I took it for testing they said 'battery is good, just needs charging'.

I suspect if you charge it they will say 'battery is 100% charged, it's fine.

I think the issue is that the new pocket testers do not load the battery. You need the old fashioned style tester that had resistors, and you could dump a crap load of energy while monitoring the voltage and current.

Project Farm did a review of testers, they did seem to work, but I prefer to see the battery do some work under load.

My trolling motor is pulling about 30amps, so fairly sure my amazon ampmeter is reading it with enough load.