Battery Question

Hi.
I have an SD300, with the original Canon battery and charger, and a second (non-Canon) higher capacity battery.
Recently, I've been experiencing the following problem:
after I insert a fully-charged battery (either one, charged with the Canon charger), I get less than 20 or so shots before the low battery icon starts to flash, and shortly thereafter, the camera gives me the replace battery warning and shuts down.
Normally, I would attribute this to a bad battery, but when it happens with both batteries, I look to the camera as the source of the problem.
So, when I was in New York a few days ago, I stopped by the B&H Camera store (amazing place!), and asked about it. The salesperson immediately said that the batteries had been overcharged, and were toast. I suppose that's possible - Canon says to charge the batteries until the green light on the charger illuminates, then stop charging. I have, in the past, left the batteries in the charger for much longer than that (as long as overnight, if I've forgotten about them), but the batteries never get even slightly warm, so I assumed that they were OK.

So, two questions:
Is the salesperson right about the batteries being toast?
If I have to replace the batteries, I'd also like to replace the charger with a "smart" charger (such as I have for my AA batteries), where I can put the batteries on charge and leave them indefinitely. Are such chargers available?

Thanks.

TTT
Anyone?

Seems like about all battery chargers have some sort of over charge protection in them.
Other wise they'd be a fire hazzard....but I could be wrong.
Batteries do develop a memory if you don't zapp em dry now and then to start over with a new charge.

Sounds about like what my SD600 does.

I had a similar problem with my SD500 the original batters would no longer hold a charge (could take about 40 shots) got a after market battery and it seems to also not hold a charge, found the outer case slightly different. put in a paper spacer to force the battery to the contacts and all is good again

Interesting thought, hnikesch. It always feels like the battery fits tightly, but that might be because it's pushing against the eject spring, and not the contacts. I'll definitely check that.

LesF wrote in post #9217397
Hi.
So, two questions:
Is the salesperson right about the batteries being toast?
If I have to replace the batteries, I'd also like to replace the charger with a "smart" charger (such as I have for my AA batteries), where I can put the batteries on charge and leave them indefinitely. Are such chargers available?

Thanks.

Hello
This site has a FAQ that I believe could be helpful http://www.bestbatt.co​m/article_a/115.htm

Hi, Jimmy.
Thanks for the link - great site.
According to what I've read on the site (particularly this and similar paragraphs: "When recharging a new battery or one that has not been used for months, your charger or device may indicate the battery has been fully charged after a few minutes. Please do not disconnect the battery and charger, because the recharging is not completed yet. The charger will recharge the battery in about 10 hours. This is not a problem. The same battery will be fully recharged within 2-3 hours next time. The battery will require 3 to 5 charge/discharge cycles before achieving its rated capacity."), this seems to indicate that I was given the wrong info by the B&H clerk. The batteries are being FULLY charged as we speak (write?).

Thanks again.