Well made battery, as durable and efficient as you can expect from a battery.
I bought two of these for my G&G M4 Combat machine Raider for an airsoft event I attended in 20012, Fit was a little tight, however with the stock extended completely it was an easy fit ( crane stock ) even when readjusted back to a shorter position.
Both lasted through a solid day of shooting ( 11 am - 4pm ) without enough juice left over for the night game, Charged well over night and lasted just as long as the first day of shooting.
Long lasting with G&G M4 Combat Machines.
Easy to hook and unhook.
I can't say I found any flaws with them, and don't expect to find any as they preformed admirably.