Batteries are likely showing signs of aging (chemical soup sluggishness)...
Though a bit anecdotal, I recently had a very similar issue on Safe electronic combination keypad with 9v battery - Voltage showed 9.7 but no matter what, safe would not dare open... After a few days of nagging frustrations a competent Locksmith told me that the voltage means nothing, and to simply replace the battery... I did this and safe then opened immediately!
Best to think of voltage as static characteristic and current as dynamic...
3 tons
