[header] How to know when you have to get a replacement battery [title] Check for excessive heat when the battery is in use. [step] A little heat is normal when batteries are recharging or working, but excessive heat can be a sign that they are dying. Notice if the battery starts to heat up significantly more than normal, or compare your suspicious battery to a newer one to see if there is a significant difference in heat. 
[title] See if your battery gets bloated or swells up. [step] Sometimes when the rechargeable batteries start depleting, the internal cell ruptures and starts leaking.