On the amazon web page farther down there are "Customer questions & answers" that might help answer your question.
Question: Can i use it for a dual battery system?
Answer: Sorry, this relay could not use for a dual battery system.
But our shop have another relay C14-500A-12V is fit for dual battery system.
May be you can check the link firstly,
https://www.amazon.com/dp/B07433DYSZ … see more
Question: can this be ran continuous?
Answer: Sorry, it could not be ran continuous.
On the other hand,
At the top of the amazon ad it says "FOSHIO Auto Start Relay Heavy Duty Split Charge Relay Switch" which sounds like your intended purpose. That makes the first answer sound like "bait and switch" to get you to buy the other part.
In the specifications it says that the relay coil is 4.8 watts / 30 ohms
Coil Resistance(Ω)：4.8W/30
At less than 5 watts, under 1/2 amp, the coil probably runs cool enough for continuous duty. Regular automotive relays, the 1 inch cube type, about the same as this one, usually take about a quarter amp and they work continuously without any heat build up.
If your scheme turns on the connection before starting the engine the peak current will be lower than if you turn on the relay after the engine is started and the alternator gets the starter battery up to 14.4 volts. On the other hand, your house battery will contribute some amps to the starting process reducing the starter battery load. Some people will tell you that's good, others will tell you it's bad. When someone offers you this advice ask them for more information, why is it good or why is it bad?
If you plan to have a house battery that consists of 4 LiFePo4 or AGM 100 amp hour partly depleted batteries in parallel connected to a school bus 3 battery starter battery bank with only 3 feet of cable that is as big around as your wrist the initial current might be too high. If your house battery is a single 75 amp hour flooded battery 10 feet away connected with AWG #6 the initial current will be lower. If the house battery is deeply depleted the resistance will be higher decreasing the peak current.
It isn't crazy to get the $11 part and try it. If your wire from the alternator to the house battery is long enough and skinny enough it could last a long time. If the peak surge current is high the contacts will weld together making it always on. At that time you could replace it with another similar or higher priced part depending on how the cheap one worked out. You must occasionally measure your house battery and starter battery voltage to see that they are different to know if the contacts are open and not welded. Spending ten times as much on the relay doesn't eliminate the need for occasional testing, in my opinion. People who have spent ten times as much will disagree.
When you buy cheap you get to keep the saved money for other purposes like gas, food. If you buy an inadequate product you might have to buy another later. That might still be cheaper.
