I can’t really help with these Panasonic battery packs, but I totally understand your frustration. I’m still using cordless phones as well and have found that the AAA cells are much better than the proprietary packs, but that my Pana phones, which are about a decade old, have terrible charging circuitry and tend to wear out the cells fairly rapidly. My phones seem to have no real charge-cutoff logic; it seems to be just a timer of some kind.
The phone might calculate a charge time based upon how long it’s been in use (i.e. talk time), as the charge time does seem to vary proportionally, but it will always perform a full charge whenever the cells are replaced or handset power is interrupted.
This means that I must fully discharge the AAA’s before inserting them into the phone or they will simply get cooked for hours. Even in everyday usage, I’ve randomly taken the battery cover off the back and found that the cells are often very warm to the touch for no good reason; they are being over-charged.
While I’m glad to have replaceable batteries, I’m rather annoyed that Panasonic cheaped out on the charging circuitry.
- Amazon Basics set of 12 NiMH 800mAh AAA’s for $12. I recommend these if you’ve got multiple handsets.
- Amazon Basics set of 8 NiMH 850mAh AAA’s for $10. I bought 2 sets of these because the above set wasn’t available a couple years ago, but the extra 50mAh is probably worthless here, if it even exists (Amazon seems to rate capacity fairly accurately, though).