Get onto your keypad and dial *#*#service#*#* and in the menu will find calibrations and tests etc...one of those options has the battery health in it, click it and it will tell you what condition your battery is in a mAh figure and will say 'good, no need to replace' or 'bad, replace the battery'.
Hope this helps, I haven't actually got the handset in front of me or I'd guide you through the menu.
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