The model 430 allows for USB charging of the receiver batteries. In the settings there are 3 choices for battery type. The rechargeable choice listed is NiMH I have many sets of NiCad batteries for my game calls. I swap out battery cartridges on my electric collar after every set because of temperature. They recharge fine for me. I use them in Garmin handheld gps’ as well. Yet, they do not seem to properly recharge, if I put them into the Astro. I can charge them at home, they are 2300 mA batteries, but I cannot make an entire weekend with one set of batteries in the receiver. Yet, if I plug in standard AA batteries, it will run several days before it needs batteries. And the NiCad batteries don’t seem to charge properly in the 430 via USB cable. Anybody have any experience or correspondence with Garmin related to this? I don’t really want to spend another 25 bucks on a single set of batteries when I have 30 Nicd’s sitting here.