Force Charge or Not Before Storage?

a few weeks? i have left mine in the garage for 5 weeks almost every winter for 12 years without even thinking about battery charge. is that a problem?

 

I guess that depends. Sounds like you already have enough to worry about and don't need to worry about your battery health.

Just keep an eye out for the coal rollin diesels at the cross walks as those should be a bigger worry in more ways than one.

 

For the hybrid battery I'd say no. For the 12 volt battery, I'd hook up a smart charger, just leave it connected.

Our 2010 was built in Aug 2009, we bought it (with about 10km on the odo) in Nov 2010, no problems. Well, with the hybrid battery, the 12 volt was dead as a doornail.

 

i have yet to put a trickle charger on. my theory is that, if the 12v is healthy, 5 weeks in 40ish f degrees is no biggie. so far so good, it is always 12.4 or better when we get home. if i ever drained it accidentally, i would consider a smart charger.

 

At least on most RC forums, generally it's recommended to discharge NiMh batteries to between 1.1 and 1 volts per cell and then refrigerate them if stored for more than a couple of weeks, doing a charge and then discharge back to 1.1/1 every month or so. However in the case of the Prius, I'd be worried to store it down near 1 or 2 bars and then after two months of self-discharge find the car unable to start. However the batteries in the Prius don't necessarily behave exactly like RC batteries. I think if you have the equipment to take the cells down to 1 volt for storage you'll extend the battery life, however you'd need a precise way to discharge the battery and recharge it. Therefore unless I had that equipment, I'd probably walk a middle ground and store it with the battery with around 50-60% state of charge - 3 or 4 bars.

Just as important for the car is the battery storage temperature. I'd do whatever I could to keep the temperature down in the car (e.g. sunshield/car cover if parked in sun, keep car in garage in summer, out of the garage in cold climates in the winter etc.).

The thing that's probably most worrying for the Prius is the battery cells becoming unbalanced with each other, from cells having different self-discharge rates. If it's a regular thing over the life of the car, you can consider one of those battery balancers (I know hybrid automotive sells one for about $400). Watching the voltages as you've done will give you an idea when this is occurring.

When the car comes out of storage, I'd take the battery charge up to as high as the Prius will let you on its first use.

Otherwise, I'd just drive the car and accept the fact that the hybrid battery will fail at some point. Don't get hypochondriac about battery health!

 

That's about on par with leaving it on a charger I think. Phantom charge is what does batteries in.

When I replaced our 12 volt semi-preemptively, someone here suggested to keep the old one for backup. I charged it up and tucked it away in the garage. Checking its voltage months later, it's barely dropped.

 

I've found the 12v batteries actually have a good lifetime to them. It probably will be good beyond 10 years. My 2008 OEM battery is still going strong. Key is to keep them charged up and not let them get weak.

 

Yeah I think it was you that suggested I hang onto the old one.

 

I would like to have decent charge say most of the blue bars, but never really had to force charge. For the 12v on Gen2 I would turn off the SKS button under the steering column.

What I see is rapid depletion if you just drive off when you get back from the trip, especially if you have A/C on. So what I like to do is turn the A/C off and let the car warm up about 3 -minutes before driving off. What happens in the warm-up cycle is the engine comes on after about 30-secs, it runs a couple minutes, giving batt some charge, and then it goes off. Now go!

 

That's common advice for any car too. Honda says something like:

Just start it and go, except when the car has been sitting a few days. Then let it idle a minute or two.

 

I rebuild batteries and have dealt with thousands of individual modules. When modules are stored at a very low SOC 10 to 20% will drop in to the 6.XX volt range. This is caused by one cell dropping out while while the other five remain above 1.2 volts each. These modules can not be recovered. I have never seen this happen with modules stored at a high SOC. So, I would recommend doing a forced charge before storing a car for an extended period.

Modules #1 and #28 just behave differently than the rest of the pack. I used to think this had to do with cooling. Can any EE's site a reason for being the end modules of a series string having a different effect?

I think what you are seeing is modules 1 and 28 have reduced capacity and high self discharge. The car has no way to "balance" cells. The battery is just one big series string. The same current flows in and out of all the cells. When driven the voltage of 1 and 28 will catch up with the rest because they have less capacity to absorb the current than the stronger cells. When the car sits high self discharge then brings the voltage of 1 and 28 back down.

Brad