What's the best charging position for robot batteries?

[pipsqueaker]

Team 771's powerpoint on the subject says that the batteries can be discharged in any position but that they need to be charged upright. I haven't been able to find any other information on this.

We're designing a new battery cart, and we need to know if charging position is a constraint. Any help?

[Michael Hill]

I wouldn't see why they have to be upright...they're not flooded. The only reason I can think is a slightly less risk of shorting out the leads through worn out electrical tape, but the odds of that are relatively low.

[Tyler2517]

One of our mentors has always said that if they can be kept upright keep them upright. Something to do with that you don't want the jell that is inside to slop any and loos contact with the plates?

[cgmv123]

They need to be charged upright to vent the gases that are generated during charging. They can be used in any orientation except upside-down.

[Michael Hill]

The only other thing I can think of is it would ensure proper venting if overcharged.

Originally Posted by cgmv123

They need to be charged upright to vent the gases that are generated during charging. They can be used in any orientation except upside-down.

beat me to it.

[Al Skierkiewicz]

Well, AGM cells can theoretically be used and charged in any orientation. Gell cells are different, slightly. I recommend that charging take place with the batteries facing up for one reason only. Any water vapor will naturally drop onto the cell pressure seals during inverted charging orientation. If for some reason, the internal pressure causes the seals to open, some of that water will be lost. This is an extremely rare event. Just my way of optimizing battery life. Lost water translates to less contact between electrolyte and plate. Less contact relates to less available current which will lead to shorter usable life.

[DonRotolo]

Exactly: Charge upright so you vent gas in the unlikely instance of overpressure venting. Otherwise it makes no difference.

[philso]

I seem to recall Enersys telling us at work that if the battery vents while upside down, it may push some of the acid out. This would be more dangerous than just venting the gasses. We use tons (literally) of the 7AHr version of the battery in our UPS' each week.

[Al Skierkiewicz]

Phil,
That is true in gel cell technology but not in AGM. The acid is "locked" into the fiberglass matrix so it is not free flowing except when the case is damaged or some other catastrophic event occurs.

[DonRotolo]

Originally Posted by Al Skierkiewicz

That is true in gel cell technology but not in AGM. The acid is "locked" into the fiberglass matrix so it is not free flowing except when the case is damaged or some other catastrophic event occurs.

Well, yes and no. The 'Glass Mat' into which the acid is 'Absorbed' can be thought of as a fiberglass sponge. Just like a sponge, if you shake it or squeeze it, liquid will drip out. In a venting situation (which is a "catastrophic event" IMHO), it is unlikely the gas will form right at the vent, so it will 'push' some of the liquid out of the 'sponge' and then it can come out of the vent.

That being said, a standard qualification test for automotive AGM batteries is to drill a series of 6 mm (~1/4") holes in the bottom of the case, and NO acid may come out at all. So yes, the acid really does stay in there most of the time.

Now that being said, charge your batteries - Gel, AGM, and conventional -upright please. Spewing acid is not a national emergency, but someone could get hurt.