HCH Battery is dying :(

[Jdesign]

First off I hope im posting this in the right section.

I have a Manual 2003 HCH that has been treating me very well. In the last year the battery has been degrading and I finally decided I should do a complete discharge and grid charge(I have a Maxx volts unit). With the fierce cold weather, and snow tires (Im in Wisconsin) my MPGs are lower than I have ever witnessed since owning the car, 50mpg a tank, to a horrible 35-40mpgs.

With that said, this is the first time I have had the battery at complete discharge. I used a light bulb to run the battery to zero as I have seen many others do online. I have a grid charger that I am using to bring the battery back up to normal voltage and have been driving another car in the meantime.

So the main reason I am posting here is that prior to the complete discharge I was grid charging at night and the battery was getting around 180-182v with 310Ma.

Now, after the complete discharge, I am now only seeing around 150v with 310ma.

Although I will allow it more time to see if I get a higher result as I just plugged it in last night and that 150v reading was today at lunch. Should I expect to see it back at 180v's by any chance?
Was the battery so out of balance that there was 1 or 2 sticks showing me a higher reading than what the battery was actually at?
I might consider pulling the battery completely and doing a full rebuild but I dont really want to do that at this time. Do you guys have any suggestions?

[Stubby79]

I see thee possibilities. You may have finished killing off a few cells, haven't let it charge long enough yet, or the cold is keeping your batteries from putting out/accepting full voltage.

Two of those are solvable without any $$/surgery.

[S Keith]

Down to zero... wow. Unfortunately, you must have done only a few minutes of research. That was briefly all the rage a couple years ago until packs started crapping out.

Given the voltage response, Stubby is probably right. Pack is done for. You took the marginal cell(s) and just drove a nail through their coffin.

It should have shot above 150V in just a few hours of charging, and cold actually causes significant voltage increase. In most cases, a successful discharge results in a higher voltage the second time around.

Note that given the inefficiencies of charging at low current and low temperature, you may need 32 hours of charging to ensure you are at true 100%.

[Baltothewolf]

Ye discharging to 0v killed a pack of mine a couple years ago. Definitely don't do that.

[cowmeat]

Falling asleep while discharging flatlined my Insight's IMA battery, and is the reason I'm driving a Volt now Not that I'm complaining!

Be careful while trying to balance cells, it's at best a band aid and at worst it causes premature failure/replacement

[Ecky]

You probably should not be grid charging or discharging in this weather, nevermind that deep discharges can be fatal for cells.

[RedDevil]

Don't panic just yet.
There are 120 NiMH cells in the pack, right?

They'd hold about 1.2 Volt each when not close to being topped off. 150 Volt under a mild charge seems OK.
When full they'd top out at 1.5 Volt each, again, 180 Volt for the full pack fully charged seems correct.

I cannot see how charging in the cold should damage them. These cells can handle close to 100 Ampere in short bursts. 310 milliAmpere is next to nothing.
I'd be careful when the voltage starts to climb as cells reach their top though 20 hours into the charge. But the pack should have warmed up by the charge by then, so even that.

You are underway with the charge anyway, if the pack is toast there is no harm in continuing, and if it isn't it is the right thing to do anyway.

I would never charge LiFePO4 batteries in severe cold, but that's another chemistry.
Talking about that:

http://batteryuniversity.com/learn/a...w_temperatures

The problem with cold charging NiMH batteries is that they appear fully charged when they're not; then you'd be at 180 Volt early, which is not the case. No worries then.

[Ecky]

The voltage profile of NiMH is different when it's cold. They probably won't be damaged from a grid charge, but a full pack won't top out at 180 volts if it's 0F, it'll be much higher and OP's grid charger may not be able to go high enough. Plus, I'm uncertain what goes on inside of them in extreme temperatures. I know my Insight's BMS does everything it can to prevent the batteries from getting low when it's cold out.

[Jdesign]

Thanks for all the great responses guys!

So I should clarify a bit. Yes the weather is cold here, but the car is inside my climate controlled shop (72F) where I am performing the discharge/charging. I mentioned the cold because I have noticed when im actually driving out in the cold, or if it sits outside for the day when I am at work, that its charging rate is diminished while driving. The temps outside here have been around (-15F)

With that being said, yes I did take the battery down too far as I failed to do enough research. Lucky for me, it did bounce back to 178 by the end of the day(24hrs) with my grid charger. Originally from 180-182v so some harm but not much. My guess is that there may have been one cell or two sabotaging the whole pack from working properly in the first place.

So moving forward I have read that there are a few guys that will do a charge/discharge a few times. Does that sound correct or is it a waste of time. Im not too worried about opening the battery up and replacing sticks if I need to, I just would prefer to avoid doing that right now. I have yet to drive the car and see if there is a notable difference in performance.

[S Keith]

Battery temperature is what matters. 24 hours is not sufficient. I'd give it another 8 hours per my recommendation above.

After another 8 hours, I'd drive it and see what happens. Given the method of discharge, subsequent cycles will only give small improvements if any. If the pack codes or recalibrates regularly, it's done.

Concerning stick replacement, I think you've likely done too little research again. Stick replacement is not a trivial exercise. Sure, the act of physically replacing a stick is relatively simple and time consuming. However, getting a lasting repair is extremely difficult. If you're cool with whack-a-mole and getting into the pack half a dozen times before it's semi-reliable, then you should be fine.

No matter what, you're looking at grid charging as preventative maintenance moving forward.

If your time has any value, you would be better served by pack replacement.