Here some experience with my new frog. I've made ~50 dives with it.
During one dive the Frog switched off at a charging level of 25% of the LS14500 3.6V Saft-Battery.
I have not noticed a battery alarm before.
A battery replacement at a charging level of 30% seems to be reasonable in the future.
Unfortunately no 3.6V batteries were available on holiday, so I inserted 1.5V Alkaline batteries.
Already from the second dive battery alarms occurred, 2.81V .. 2.73V. I've changed the Alkaline batteries all 3 - 4 dives.
I.e. it is possible to use 1.5V batteries, but only as exception for a few dives.
Battery changes should be done very carefully, because the mechanical construction (metal plug vs. plastic screw thread)
is very damageable. Use a screw drive instead of a coin. Do not twist the metal plug.
For a future Frog successor I'd like to propose to use rechargeable batteries instead, as used at the OSTC 2N.
Or a less damageable mechanical construction.