Bad Reef Racer Battery

[scott216]

I just got a reef racer and I think my 7.4v 1100mAh 6-cell NiMH battery is defective. RR would only run for a very short time then the battery would die. I put the battery on a CBA battery tested and discharged it at 3.3 amps (3C). The voltage dropped off very sharply after 2 minutes. I only got 125mAh out of it before I reached the 5.4v cutoff voltage. I wasn't sure what a good discharge rate was, I don't how many amps the RR motor draws.

See attached discharge graph.

Do I have a defective battery?

--Scott

[Ctonez]

sounds like a tired cheapo NIMH pack to me. Your graph is typical of NIMH output.
1100mah is very little capacity, even in a Reef Racer. Are you pretty familiar with NIMH charging? How many charges does the 1100mah pack have?
Peak it just before you run...ideally the batteries will still be warm when you put them in the boat.
For $20 I got a small 2S Lipo pack for my Reef racers and Mini-v's. Lots more fun! But running Lipos does require a bit of knowledge/data/gear be obtained to be safe.

[scott216]

I only charged the pack a couple of times. I'm learning about LiPo, my RC planes use them. I guess I would need a LVC for the reef racer.

[Rex R]

how soon we forget..., it is not unusuall for a new nimh pack to act this way. it normally takes a few charge/discharge cycles to 'wake' them up. try running the pack some more., if it doesn't get better, then yes it may be bad. I would guess however that it is more likely that the pack sat on a shelf for some time before you bought it and just needs re-conditioning.

[scott216]

Thanks. I'll cycle it a few times and see if that helps.

[scott216]

how soon we forget..., it is not unusuall for a new nimh pack to act this way. it normally takes a few charge/discharge cycles to 'wake' them up. try running the pack some more., if it doesn't get better, then yes it may be bad. I would guess however that it is more likely that the pack sat on a shelf for some time before you bought it and just needs re-conditioning.

That's worked. Now I'm getting 735mAh before the 5.4v cutoff. Attached chart shows performance before break-in (red line) and after I cycled the battery a few times (black line).