I was in Lidl earlier & they have reduced the battery/charger set by 30%, they are now just £9!
The set is cheaper than just the battery (£12.99). 
Purely in the interests of product research I bought one!
Took it apart & these are the details of the internal cells.
Parkside INR 18650E 2000mAh 3.7v Li-ion 20180304 YG
There are 5 cells so they are not really 20v batteries, more like 18.5v.
Googled them & found a site where someone thoroughly tested them.
http://budgetlightforum.com/node/66074
Now I'll not pretend to understand much of his results but they were quite good apparently they compared closely to a Samsung INR18650-20Q.
This is giving me an idea. I have some old Hitachi 18v nicad batteries that are done. I can gut them & fit the internals of the lidl battery. Then to charge them I can fit the internals of the lidl charger to the body of the broken hitachi charger I have. That way I am charging the lidl battery with the lidl charger, just in different casings.
There's no reason why this couldn't be done with any other make of 18v tool, you just need a spare charger. The only issue would be if the Li-ion batteries are too long to fit into your old casing. Then you would have to do some butchery!
The set is cheaper than just the battery (£12.99). 
Purely in the interests of product research I bought one!

Took it apart & these are the details of the internal cells.
Parkside INR 18650E 2000mAh 3.7v Li-ion 20180304 YG
There are 5 cells so they are not really 20v batteries, more like 18.5v.

Googled them & found a site where someone thoroughly tested them.
http://budgetlightforum.com/node/66074
Now I'll not pretend to understand much of his results but they were quite good apparently they compared closely to a Samsung INR18650-20Q.

This is giving me an idea. I have some old Hitachi 18v nicad batteries that are done. I can gut them & fit the internals of the lidl battery. Then to charge them I can fit the internals of the lidl charger to the body of the broken hitachi charger I have. That way I am charging the lidl battery with the lidl charger, just in different casings.
There's no reason why this couldn't be done with any other make of 18v tool, you just need a spare charger. The only issue would be if the Li-ion batteries are too long to fit into your old casing. Then you would have to do some butchery!


But I've come up with another plan. Make up an adapter by inserting the battery connection part of the lidl charger into the empty Hitachi battery case, Then I can use the lidl batteries as they are, just clip them into the adapter. I've bought 4 battery/charger sets so I have 3 spare chargers to play with!