just a thought, as a fisher person, I make me own cages for fishing, I use wheel balancing weights, I just go down to me local garage, and go though their buckets, just a thought a bit off hot glue, job done,
Only add weight to balance a plane as a last resort. You are far better off moving your equipment to obtain balance than adding weight. Lighter planes fly better and suffer less damage in a crash.
Those are the weights I use when I have to.....cheap to buy on ebay complete with super sticky pads attached. Agree with @Merv - not having to use them is always better but if you cant re-position a battery to balance, a bigger battery to balance is preferred over adding dead weight.
The heavier your craft, the more inertia it has to damage the airframe in a crash.
The weights will work, but there is a price to pay. @CarolineTyler has a better idea. If you have to add the weight, make it work for you so you also get an offsetting benefit if you can.