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I am not sure I agree with Tim here,, which is unusual actually,, if it were me, and my batteries, I would be leary fo doing that , if you mean using a Para board to gang charge,,
ESPECIALLY if they are different C ratings, and such,, I just dont think it would be wise,,

I am assuming you are talking LiPo packs,

I have a bunch of 4 cell batteries, some are 2500 mah and some are 2700 mah. Can I charge them all at the same time from a storage charge to full charge?

Now I see they have a 2800 mah 4 cell which will compound the problem if I buy some of them.


Thanks,
MM

I have a quad charger; 4 ports x 80W max each. I think the same brand has a 4 x 100 out now. I balance charge 4 packs at once. Heck, I charge my RC sailplanes, and my transmitters, and a lead acid battery for the winch all at once. I just have to pay attention to the settings.
If you have all 4S packs, it's easy-peasy.

Other than that, you could discharge "flown" packs to a set voltage, one at a time (or for that matter CHARGE them lightly to storage voltage individually), then hook them up on a para-board, and charge all at the same time.
The issue doesn't change though unless your charger with one output has some balls (watts)....If it's limited in amp delivery, you're still going to take a long time to fill your 10,000ma+ battery (4x2500+ma)...

So, to save time, you either need to parallel charge on one output at high amperage (1C) for a reasonable charge time, or like me get multiple outputs and keep the battery sizes smallish. Essentially you are doing the same thing either way. You need some watts to fill some tanks.

Since I still fly RC, and have to charge LiIon, LiFe, NiMH at the same time, the Quad charger makes sense. And 4 LiPo's is easy too.



R,
Chris

Packs of different capacity will discharge to different voltages so I guess I can't charge them together after flying.

As noted above, you can adjust the voltages to a set point so that the voltages are close.  Capacity is not really a factor if the voltages are similar.  I have fairly new TP 2800s and a midlife TP 2700.  At the end of a session the 2700 will be a bit lower in voltage and corresponding, it has about 20 - 21% left as per my PowerLab 8 reading where the newer 2800s have about 24 - 25% at slightly higher voltage.  They are probably close enough, but with a few trial, about milliamps into the 2700 will bring the voltages to matching. Then all can be storage together.  Matching cell counts and matching (close) voltages.