Graco Pack'n'Play Owner's Manual page 20

Keep the batteries out of children's reach.
Any battery may leak battery acid if mixed with a different battery
type, if inserted incorrectly (put in backwards) or if all batteries are
not replaced or recharged at the same time. Do not mix old and new
batteries. Do not mix alkaline, standard (carbon-zinc) or rechargeable
(nickel-cadmium) batteries.
Any battery may leak battery acid or explode if disposed of in
fire or an attempt is made to charge a battery not intended to be
recharged. Never recharge a cell of one type in a recharger made for
a cell of another type.
Discard leaky batteries immediately. Leaky batteries can cause
skin burns or other personal injury. When discarding batteries, be sure
to dispose of them in the proper manner, according to your state and
local regulations.
Always remove batteries if the product is not going to be used
for a month or more. Batteries left in the unit may leak and cause
damage.
Recommended type batteries—alkaline disposables. NEVER mix
battery types. Change batteries when product ceases to operate
satisfactorily.
TROUBLESHOOTING: If your device is not functioning
properly, check for the following problems:
1. No batteries in electronics module.
2. Batteries dead.
3. Batteries in backwards—check "+" and "-".
4. Corrosion on battery terminals. Rotate batteries in place
against terminals, or clean with sandpaper or steel wool if
corrosion is severe.
5. Batteries too weak.
For Safe Battery Use