This is the Sterling ProCharge Ultra's on battery temp sensor. It's 10' long, but could be extended with a typical 6P2C male to female RJ11 phone cable or with an RJ11 in-line coupler. The sensor is using the two middle terminals as would the typical red & green two wire phone cord.
Temperature sensing of your batteries can be very important to the longevity of a bank especially with valve regulated lead acid batteries such as AGM/TPPL or GEL. The hotter the climate you are in the more important temperature compensation is. Temperature compensation is more critical as temperatures rise rather than fall. As the battery temperature goes up, the battery charging voltage must come down. As battery temperatures drop the charging voltage can go up.
Heat is one of the number one enemies of batteries. If you have them in an engine room, which is not advised, you really do need a charger that has temperature compensation to reduce the charging voltage when the batteries begin to heat up. If your batteries can regularly exceed 80F then you'll ideally want a charger with temperature compensation. Earlier temp compensation on some chargers was sporadically successful at best, bordering on "dumb", as in not very smart. With newer technologies they can be accurate to within a degree or two which is more than enough.
Any charger that does not offer ON THE BATTERY temp sensing is simply NOT a "smart" charger.. Beware that many charges that claim"temp compensation" are doing this via ambient temperature at the charger. If the charger is in a cool spot and the battery in an engine bay you will COOK your batteries. NOT SMART... The Sterling ProCharge Ultra comes standard with an on-battery temp sensor.
Sadly the term smart charger is bandied about these days like a ping pong ball. I think Deka / East Penn, one of the largest US battery manufacturers, cautions well on "smart" chargers.
Quote = Deka / East Penn
"Unfortunately, many chargers on the market claim to be gel/VRLA “friendly” or “OK for sealed batteries”, but are not. Some overcharge the batteries, while others may not fully charge the batteries. Some chargers claim to be “smart”. Some “smart” chargers do a good job, others do not. The best choice of charger often depends on the application.
Almost all applications require temperature sensing and voltage compensation. Beware, many chargers measure the ambient temperature which could be significantly different from the battery’s internal temperature."
The bottom line, if a charger claims to be "smart", and it does not have a temp probe that can be physically mounted to the battery bank, IT IS NOT A SMART CHARGER.