Let's look at the Dungeon Masters Guide first. Rods, staves, and wands encountered during the course of an adventure typically have a number of charges as follows:
rods 50 charges minus 0 to 9 (d10-1)
staves 25 charges minus 0 to 5 (d6-1)
wands 100 charges minus 0 to 19 (d20-1)
Basic/Expert D&D differs from this and from itself. According to the Basic rulebook, "Unless otherwise specified, a wand, staff, or rod will contain 1-10 (1d10) charges when found." Now that's a difference! In contrast, the Expert rulebook states "Unless specified otherwise, a wand has 2-20 (2d10) charges and a staff has 3-30 (3d10) charges when found, and each use of a power will use 1 charge." Either way, the difference in wand charge capacity between Basic/Expert D&D and AD&D is vast. I propose something a little different.
For each rod, staff, or wand, the charge capacity is determined randomly.* This is the maximum number of charges this particular magic item can have. Once the charge capacity is known, the exact number of charges can be generated.
1. Maximum 16 charges (roll 4d4)
2. Maximum 36 charges (roll 6d6)
3. Maximum 64 charges (roll 8d8)
4. Maximum 100 charges (roll 10d10)
Those who dislike rolling that many dice can use the following table:
1. Maximum 16 charges (roll 1d4 x 4)
2. Maximum 36 charges (roll 1d6 x 6)
3. Maximum 64 charges (roll 1d8 x 8)
4. Maximum 100 charges (roll 1d10 x 10)
The advantage, as I see it, is an increase in the middle range and an elimination of one charge wonders.
* This can vary by category (e.g. wands), type (e.g. wands of lightning), or individual item (e.g. the wand of lightning I inherited from my great grandmother) as desired.