Phone battery is it fu*ked?

Exactly. They normally have AAA batteries that can be replaced.

My home gigaset handsets are on their third set of batteries. Changed last week most recently. YMMV.

Counter intuitively low capacity NiMh cells are better for DECT cordless phones than high capacity ones. The low capacity ones are much more tolerant of being left on continuous trickle charge.

My two original Panasonic DECT handsets were still going strong after about 10 years on their original batteries. I only replaced them when I bought two more handsets and just put new batteries in all of them.

Yep. My Panasonic DECTs are coming up to 13 years old with the original batteries, and phone calls lasting an hour are no problem.

I bought a 'refurbished' iphone 3 years ago. On receipt the 'Battery Health' was at 86%. Over those 3 years I have recharged to 100% each time. Battery Health has now plummeted to 85%. Hence it doesn't seem to be a problem - for me, given my usage pattern.

The batteries use a two phase charge method. Phase 1 is CC and inserts 80% charge level. Phase 2 is CV and is the topping charge (asymptotic to 100%)

The Phase 2 activity takes longer, as the current flow during Constant Voltage phase tapers off, and the shutdown of charging quits at a certain percentage of the original current flow level.

(Figure 1)

Paul

The 80% point, is defined as the point at which a CC (Constant Current) charging method hits Vmax (the maximum allowed voltage for the cell). It is the amount of charging achieved during Phase 1. 80%.

More info here.

When you use the 80% method, it is not the 80% we are interested in. It is the shape of the "Phase 1 charge cycle only" charging method. we're spending as little time as possible at Vmax, and that results in an approximate 80% fill level. We get more charge cycles due to the reduced wear by not running at VMax for long periods of time. It touches Vmax (as the detection of the 80% charge termination point), but then the pack begins to relax right after that.

People who leave their laptop plugged in, depending on the charging policy that can have an effect on the pack lifetime. At least the removable packs can be replaced (with something which may or may not use quality cells). Any equipment with glued-in items, where there is a danger of breaking the glass, we adopt more conservative charging policies for those, as we're not excited at the prospect of using our spudger to get inside. .

Paul

You've made me take the back off for the first time!

To my surprise it isn't a pair of AA-sized cells but a Siemens-branded rectangular Li-ion with a capacity of 700mAh and contacts at the end of one of the long sides..

How low are we talking about? I've used 450 and 600 mAh cells. Currently using 900 mAh as that's what I had to hand. Lower ones are harder to find.

Presumably the lowest capacity you can easily find. I suppose low capacity cells are less tightly packed and can dissipate heat more easily from each layer.

Poundland has been known to be a source of low capacity cells. Other pound shops are available.

Somebody caught the Gigaset C430 deliberately overcharging and did a firmware fix: