"Do I have to remove the battery caps to prevent gas build up while charging?

[MetroMPG]

Someone contacted me via e-mail with with this question. Posting here for the benefit of future Google searchers, and in case anyone else wants to jump in with info/advice...

My name is *** and I come from Slovakia. I am really
interested in EV conversions like your one and I decided to build something
simillar. I like the way you converted Geo Metro to an EV with just
little money.

The problem I have is about recharging batteries. As I could
see, you are using lead acid flooded batts. But I allways heard, that I
have to open all the caps before charging, like by car batteries, because by charging escapes hydrogen, which can cause an explosion. My first EV
Marek's 1981 Jawa Babetta 207 (well, it is just electric moped )
uses lead acid flooded battery and before charging I allways open 6 caps
on single 12V battery. But I can´t imagine opening that plenty of caps on
every battery.

[MetroMPG]

I replied:

I've never heard of the requirement to open the caps while charging golf cart type batteries we use, and don't know of anyone who does.

Perhaps it is a difference in cap design?

But the gas is able to escape these batteries while they are closed (which is the reason some people build enclosed battery boxes & vent them to the outside). The seal is not air tight. In fact electrolyte can seep out if the battery is not sitting upright.

[MetroMPG]

Response from Slovakia:

So if it´s a golf cart battery, I don´t have to open caps... But here in
Slovakia electric golf carts aren´t very popular, so there aren´t any
golf cart type batteries in shops. But do you think, that I could use
starting Lead Acid Flooded batteries instead, or should I invest to more
expensive types, e.g. Gel, or AGM?

[MetroMPG]

Any deep cycle flooded battery would work in a golf cart - I'm sure there are other applications where they are used in Slovakia that are more common than golf carts. (Industrial floor cleaners, scissor lifts, etc.)

I wouldn't use a "starting" battery though - if it's not a deep cycle battery, you won't get a very long cycle life from it.

Gel or AGM gets around the gas venting problem, with the advantage you can position them without having to keep them upright.

Ben's using such batteries in his converted motorcycle: http://ecomodder.com/forum/showthrea...rsion-599.html

[Thymeclock]

Originally Posted by MetroMPG

I replied:

I've never heard of the requirement to open the caps while charging golf cart type batteries we use, and don't know of anyone who does.

Perhaps it is a difference in cap design?

But the gas is able to escape these batteries while they are closed (which is the reason some people build enclosed battery boxes & vent them to the outside). The seal is not air tight. In fact electrolyte can seep out if the battery is not sitting upright.

The old style batteries had removable caps, but as far as I know they were vented. In fact I would recommend that you not remove them while charging the battery. The reason being that while charging the electrolyte typically will bubble and spew minute quantities of acid out of the battery. At the very least this might result in rust from the unseen presence of stray acid.

You might want to check that there is the right level of electrolyte in the battery before charging it; but leave the caps on while charging.

[Bill in Houston]

deleted- too late to the party.

[MetroMPG]

Originally Posted by Thymeclock

while charging the electrolyte typically will bubble and spew minute quantities of acid out of the battery.

Good point. And sometimes it may be more than minute quanties.

EG. depending on how well balanced the pack is (the ForkenSwift's hand-me-down packs aren't!), some batteries may bubble vigorously while the laggards come up to a high enough voltage before the charger decreases output. (Assuming a smart charger.)

[Ryland]

I would only ever remove the caps to check water level, if the batteries are dead, stored for a while or something else odd, only fill them enough to cover the plates as the fluid level will rise as they charge and will rise as it warmed up from charging, once they are fully charged top them off to the recommended level.
all caps are vented, if they were not then they stress the battery case, you can get caps that have little fuel cells in them that turn the hydrgen back in to water, but even those are vented.

[puddleglum]

I have heard heard the recommendation to remove the caps when charging before, but, it was many years ago. I suspect that it is an "old wives tale". No battery manufacturer that I know of requires it and neither do any of the electric forklift manufacturers that I deal with. As had been said, It probably does more harm than good.

[Bill in Houston]

I mean, in your car, the battery gets discharged and charged, and we don't mess with the caps while that is going on...