As batteries get older they drop capacity with a full charge. A three year old battery, for instance will be doing good to charge to 85% of what it originally held.
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When changing out batteries there are vastly differing qualities of batteries. A battery may be new but old stock and already dropped in capacity. Best thing to do is take it almost all the way down and then do a full recharge a couple of times.
As batteries get older they drop capacity with a full charge. A three year old battery, for instance will be doing good to charge to 85% of what it originally held.