If you’re concerned about buying a third-party battery for your charger, my experience with a Pearstone has been fairly positive so far.
Over our train trip through California in December and January, I left my camera battery and charger connected to the in-seat power outlet on the southbound Coast Starlight. I had the battery and charger since I bought my Canon 20D camera in November 2005.
Thankfully, the battery is pretty common as it was used in almost all Canon digital SLRs until the 40D but was the battery for the 5D Mark II. Since there are so many of those out there, it’ll be a while before these batteries become rare. However, original manufacturer batteries can be expensive, so it’s tempting to look for third-party brands.
To replace my lost battery and charger, I bought the Pearstone BP-511A battery and the matching Pearstone Compact Charger. I’ve used it for about four months, and so far, I haven’t noticed any diminished performance. Only time will tell if it will hold up to repeated charging cycles. My original battery would last for well over 1,000 exposures, even after over seven years of fairly regular use.