Here is some good information in GEL batteries, in case people consider them. They must be charged more slowly than deep cycle lead acid batteries or they will outgas and be damaged. The outgassing happens on deep cycle wet cell lead acid batteries, but you add distilled water to them to take care of that.
This is from a battery FAQ at:
Support - FAQs | OPTIMABATTERIES
15. What is a Gel Cell Battery?
A gel battery design is typically a modification of the standard lead acid automotive or marine battery. A gelling agent is added to the electrolyte to reduce movement inside the battery case.
Many gel batteries also use one way valves in place of open vents, this helps the normal internal gasses to recombine back into water in the battery, reducing gassing.
Now to answer your question about outgassing:
Normally, if you charge them at the specified rate, they should NOT outgas. The gasses in theory should be reabsorbed. However, they WILL outgas IF you charge them at too high of a rate. In that case, the one way valve will let the gas escape for safety, but if you are generating gas you're damaging the battery.
"Smart chargers" (like those supplied with the contest) are SUPPOSED to charge them at a low enough rate that will NOT cause them to outgas. (That's why they take so long to recharge.)
However, I have NOT personally run any tests on the supplied chargers, and as rookies we haven't experienced any battery failures to date so we have no data on their lifespan. I just have to assume FIRST insured the selected chargers are designed correctly for the supplied batteries.
BTW... If you look up the battery specs, you see you can VASTLY improve the total number of cycles on the batteries by keeping them fully charged and NOT deep cycling them. These are NOT NiCds. You shorten their lives by something like a factor of 10 or more by running them into the ground before recharging them. You should always recharge them fully after each use. So make it a habit that EVERY time you use a battery, even for a short test cycle, you put it back on the charger overnight afterwards.
The batteries also lose a small amount of charge per month to internal discharge resistance. Therefore, to keep them in best shape, you should try to stick each of your batteries on the smart charger overnight at least once a month to keep them "topped off". The charger shuts itself off when the battery is fully charged, so you won't harm them even if they seem fully charged when you put them on it (or if you forget and leave one on it for a week or two
).
We serial number our batteries, and keep a "battery log" posted on the wall in our storage room by the charging station so we know the charge history of each one, and keep one on the charger at all times in a rotating fashion.
