Hi folks Is it safe to put standard c size NICAD rechargable batteries into a compaq 4/25 laptop battery pack to replace the dead nicad cells? Is there a smart circuit inside? any help appreciated!!!!!

I have never seen a battery pack that uses C cells, most of them use AA size. But before you replace the cells look at the pack and see what type of cell they are using. Most laptop battery packs use lithium ion or nickel metal hydride cells. If they are litium ion or NMH, do not replace them with NiCads.

Also i'm not sure how you would secure them together. battery manufactures use spot welders to weld the contacts together, you can't just solder those things, the heat will distroy the cells.

I would say it is unsafe. Not only can you run the risk of personnel injury or death, you can ruin your equipment and home. Almost every laptop battery has smart controls. I have tried to tear them apart the get the industrial size and for all the time and trouble it is easier and safer to buy a new battery. I read it wrong and answer it wrong too. So get off my case you goober.

Thanks for the help will buy a new battery instead.

As a possible alternative you could use an external battery pack connected through the ac adapter connector. Drawback you need a pack with a odd (higher) voltage. There are companies that rebuild battery packs. Actually you could rebuild your own pack but you should replace all the cells with the same type. Solder tabbed cells are available.