It depends on how big the lipos are, and how many of them you want to charge on the day. There are three main varieties:
1) Starter batteries. The most common and cheapest type. Lots of very thin lead plates, sometimes perforated to maximize surface area. Designed to deliver bursts of very high current, which is exactly what they get called upon to do while starting a car. This type of lead acid battery really dislikes being anything other than 100% full. Even just a few deep discharges are enough to kill one of these.
2) "Hybrids" or dual-use. Still meant for use as engine starters, but somewhat more robust with thicker plates. Capable of dealing with some amount of deep(er) discharge, though going under 50% is still a good way to destroy "hybrid" relatively quickly. More expensive than "type 1" but not as expensive as "type 3".
3) Deep cycle. Heavy bastards with massive thick lead plates. By far the most expensive (of course!). The really, really good ones can take considerable abuse, defined as discharging down below 50%, but given the expense of the battery it almost doesn't make sense to mistreat them.
As an example, charging a 3S 2200mAh from storage voltage (3.85V/cell) to full requires approximately 1300mAh to 1400mAh from a 12V source (~85% efficiency). A 100Ah deep cycle AGM battery, which is about as good as it gets in this scenario, could charge dozens of those without trouble. It would set you back about $300 and weigh ~30kg or so. Bad backs not recommended.
Let's say we pick a more manageable 50Ah battery and decide never to discharge it below 80%, in order to prolong its life. That would mean it could only do 10Ah worth of charging before it needed to be brought back home and discharged itself. 10/1.3 = about 7 of those 3S 2200mAh packs. If they were being recharged after a good long flight (down to 20% left in the lipo), the 50Ah battery might only be capable of 4 or so recharges if we stick to the "always at least 80% full" rule.
If the lipos are even smaller, like say 2S 500mAh packs, virtually any car battery can keep cranking them out all day. Big lipos are far more problematic. A 6S 4000mAh pack will suck around 8Ah out of a 12V source to charge. Do that twice, and many "starter" batteries will no longer start (the car). Even a 100A deep cycle battery could only cope with around 6 such charges, unless it's discharged below 50%, which constitutes abuse.
... and that's why I bought myself a little eBay generator to try. It's a 1000W 58dBa jobbie, and I brought it to the field last Sunday. It's reasonably quiet as these things go, but still too annoying around people (it would annoy me!). I took it over to the side of the field, near the heli area shrubs, and I think the noise was basically gone back where most people park their cars and chat. I'm still not sold on the idea, because carting around the generator is not exactly convenient either, but it's easier than a 100Ah deep cycle back-breaker, which still needs charging at the end of the day.
Perhaps the club could think about installing one or two semi-permanent enclosures (three-sided steel boxes) to muffle the sound of small generators, with "charging tables" nearby. If such an installation was done over near the gear container, I reckon it could be made almost inaudible, and IMHO it would enhance the club.
Just an idea
