this link should show you a video on how to do it.
plus you will be able to read up on it just below the video.
its not saying its a Ls.but see if this is the one.
The video above shows you how to replace the battery in your 1999 Chevrolet Monte Carlo. We recommend changing the battery in Chevrolets every 4 years. Although some batteries last much longer, most batteries begin breaking down chemically after four years, so you could experience dimmer headlights and other negative effects before you have a dead battery in your Monte Carlo that you need to replace.
Replacing the battery in your Monte Carlo involves removing the terminals. When you reconnect the terminals, your radio presets are likely to be cleared out. In some Monte Carlos, you may need to re-enter a security code to get your radio to work again. Check for this code in your owners manual - it will usually be either a sticker or small card in the booklet. If you can't find it, call Chevrolet and they will give you the code for free. In many Chevrolets, the transmission "learns" how you drive over time and makes adjustments, so you may experience altered driving dynamics as your car re-learns your driving style after changing the battery.
Battery Replacement 1995 1999 Chevrolet Monte Carlo 1999 Chevrolet Monte...
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how to change the battery in my 1995 Monte Carlo Ls Google Search