David Scheidt wrote:

18V lithium ion batteries consist of 5 cells in
series, to make the the 18V. Bigger batteries
(the 4 and 5 AH ones, probably; I don't know
ryobi's line well) have two sets of five cells
in parallel (5s2p is the common notation).
If the design supports it (again, I don't know
ryobi), you can draw twice as much current,
which lets you have more powerful tools.

Page 4 in the charger's manual (BCL14181H),

Ah "No. of Cell for Battery"
--------------------------------
1.3 5
1.4 "
1.5 "
2.0 "
2.4 10
-- 2.5 5
2.6 10
4.0 "
5.0 "

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