Recently I went to bunnings to purchase some new AA rechargeable batteries for my solar powered movement detector lights. They only had regular rechargeable AAs.
They guy in charge said they wouldn't work in a solar charger. Why would he say this. I actually put some regular ones in weeks later and they do work and do recharge.

G'Day Carl,
Possibly what he was getting at is the fact that normal chargeable AA's are rated at approx 2500mAH.
The normal solar devices you mention probably were designed for 600mAH, as thats all the little solar panels could hope to charge.
So, technically the cells you purchased in this equipment will never get fully charged, so not really suitable.
Bigger is not always better.
Unless of course you are talking about a solar array with proper regulator, then the cells would work fine.
JJ

Not only this but the charging and regulating method depends on the battery chemistry. NiCAD, NiMH, AGM, Lead Acid, LiCoO, LiFePO4,etc all have their own preferred way of being recharged and if you connect a battery to the wrong charger, it will not necessarily like the idea and you may get memory effect, failure to fully charge, overcharging and other problems.

I have two 200Ah 12 volt LiFePO4 batteries that I use for camping. These have ten times the density of an equal-sized lead acid battery, yet weigh 25% as much. The voltage remains at 13.5V for almost the whole charge, which is handy for devices such as camp fridges which turn themselves off when the voltage reaches 10V. Most other battery types see their voltage fall on a sliding scale with continued use which isn't as useful. But these batteries require a dedicated type of charger to recharge correctly.

The downside is the cost. The upside is that I can run my camp for more than a week without recharging the batteries but hooked up to the car via a DC-DC converter and a 350W solar panel, the power supply is almost endless.