The TT-7000 lithium battery has a minimum of 500 recharge cycles. If the device is recharged and reused every week, this would represent a minimum of 500 weeks (over 9 years). After this time, the battery will continue to work however the battery life will be reduced slightly.
The minimum number of recharge cycles for the TT-7100 non-lithium battery is 300. This means that the battery can sustain 300 full discharge-recharge cycles, roughly over 5 years.