Squidge said:
I believe its the "Battery capacity to 10%, then recharge" that actually kills them sooner.
Then again, I know very little about batteries, so someone please correct me
One of my other hobbies is electric vehicles - so I know a bit about batteries from that - and I think the knowledge mostly transfers down to this size of battery as well.
1) Yes, a deep discharge cycle is generally going to kill a battery sooner (i.e. reduce it's number of cycles). One normally talks about percentage depth of discharge - so Squidges 10% example would actually be 90%DOD. Some of the best batteries for EVs at the moment are Lithium Iron Phosphate (LiFePO4) - at 70%DOD they have 3000 cycles at 80%DOD they have 2000 cycles. In other words the deeper you discharge them the sooner they die.
2) Different chemistries of batteries (lead acid, nickle metal hydride, lithium) require different charging characteristics and have different "self discharge" characteristics (i.e. how long you can leave them on the shelf before discharging).
3) A battery can be damaged by discharging it too deeply and also by leaving it in a discharged state. The purpose of the trickle charge is to keep the battery fully charged and to stop it falling into a damaging discharged state. However, Lithium batteries self discharge much more slowly than other chemistries and I've also heard that it's best to store them at 50% DOD rather than fully charged.
All of the above characteristics are actually taken into account by the engineer who designs the charging circuit for the electronic device. The better engineered the device the less likely you will be to fry your batteries by leaving them in while the power is connected. Like with most technology early models are more likely to be less well engineered than later ones (because less information and knowledge is available for those earlier models).
All this is a long answer for saying - I wouldn't worry too much about leaving your batteries in when the power supply is on.
If you want to be cautious then personally I'd follow this usage pattern:
Re-charge your Pandora as soon as possible after using it on battery power - even if you didn't drain it all the way down. (remember that statistic of 3000 cycles for 70% DOD vs. 2000 cycles for 80% DOD)
None of this answers whether the device will be able to be used on external power without batteries - this is much more down to the design team. I have electronic devices that work only with batteries installed and those that will work with power supply only.
However, personally, with the size/cost of this battery and the size of the current draw I'm not going to bother being careful at all - I'll let the engineers figure out the charging and low voltage cut off parameters.
It's different with EVs where the batteries even for a moped can cost anywhere from $500 for "cheap" lead acid all the way up to $3500 for the latest and greatest LiFe batteries with 3 years warranty!
I did some reading up on Li-Ion batteries for laptops a while ago, and the information i could find was that Li-Ion batteries do not like sitting all charged up in a laptop, since a little current is provided to keep the battery charged.
This charge builds up the crystals that increase the resistance of the battery and thus lowering it's capacity.
These crystals form when charging, and disappear when discharging.
However since you never fully discharge a li-ion battery (and neither should you) not all crystals disappear, this is (if what i am told is correct) what causes the batteries to age.
The advice I got from my electronics teacher a couple of years ago was to let the (in this case, laptop) discharge fully once in a while, since the protective circuit in the batteries would cut of before you have drained the batteries to such a state that they take damage.
Or to take out the battery, if I was going to use the laptop on AC for a longer period of time.
