# Why we can not recharge alkaline batteries to their former voltage values

When a 1.5V alkaline battery drops to around 1V, it is usually insufficient for the operation of most battery-demanding technological devices. Couldn't batteries that have fallen to 1V and are now "useless" be used to return another battery like them to its original 1.5V value?

Isn't there a way to use the charge in these batteries when they drop to 1V or below?

• You cannot directly use a used battery to recharge another one. Anyway, if you put multiple used batteries in series, the combination may work to some extent. For example, if you put three 1V batteries in series, that will make 3V and may light an LED. Commented Jun 23 at 13:24
• Yeah but I won't be able to fit 3 batteries in series to the place for 1 battery in a battery socket in a device.
– kaan
Commented Jun 23 at 13:28
• The main problem with this (continuing to use batteries with significantly reduced voltage, for whatever) is that most of their energy has been spent. The voltage will continue to drop quickly when under any load. Otherwise, you are right, one could simply have two with, say, 0.75V in series and continue to drive devices with them. If they could be used that way for significant time, there would be fixtures for that setup. But it's not worth it because they are practically empty. Commented Jun 24 at 14:10
• This page has a few discharge/voltage charts; the ones for low currents (100mA) show the most impressive drop after they fall below 1.0V. (For higher currents, the inner resistance leads to a drop below 1.0V earlier on, when there is still more energy left.) Commented Jun 24 at 14:20

You actually can recharge alkaline batteries, but....

You can only recharge them maybe five to ten times maximum before they stop holding a charge. While the chemistry of alkaline batteries is reversible (like most electrochemical reactions), the electrodes don't re-form in the same physical shape they were in originally. This leads to parts of the electrodes breaking off (gradually decreasing capacity) or shorting out entirely (immediately destroying the cell). This means that after a few charge cycles, the battery won't hold enough charge to be useful anymore.

Additionally, you can't charge them very fast; applying too much charging current, instead of charging the battery faster, will start electrolyzing the electrolyte. With the electrolyte being mostly water in alkaline cells, this produces oxygen and hydrogen gas, increasing the pressure in the cell until it, eventually, bursts open and begins to leak electrolyte. This isn't as violent or dangerous as what can happen with lithium batteries, but it does ruin the battery.

Secondary cells (aka rechargeable batteries) have electrodes designed to be regenerated, both in terms of the choice of chemistry and in terms of the physical construction. That doesn't mean primary cells can't be recharged, but it does mean they won't recharge as easily as secondary cells.

• Can you explain why they will stop holding charge eventually and why they might leak ?
– kaan
Commented Jun 23 at 13:28
• @kaan Why they stop holding charge eventually is explained in the answer already--how the electrodes don't regenerate in the same shape. I'll elaborate on why they can leak too, though. Commented Jun 23 at 13:30
• Long ago I saw alkaline batteries sold as "semi-rechargeable". Commented Jun 23 at 22:00
• I used to have a charger designed specifically for normal alkaline batteries.  It worked reasonably well: I got several more charges out of each battery, though as you say the capacity dropped each time.  (Needless to say, you should NOT try to recharge alkaline batteries with a normal battery charger designed for Li-Ion/NIMH rechargeables.) Commented Jun 24 at 17:54
• @gidds I still have one of those... at some point they just stopped selling them. probably because the battery does tends to rupture at some point, either while charging or (in my experience) after it had been put back into use. Not terribly messy but it left white caked residue and could possible damage whatever device it was in at the time. I think one of my rechargers stopped working because of this. Commented Jun 24 at 18:11