Syntax Error asked - 'From its physical specifications, would this make a good dummy load?'

It depends what the specification for your dummy load is, and what you mean by stable. 'Battery testing' is one application, but 'other purposes' leaves rather a lot to the imagination.

Stability. Over time, and/or over temperature? Loading a battery with a fixed resistor will mean the load current varies as the voltage reduces. So I can already assume you are not testing at a precise load, just in a general ballpark. If you are measuring the battery current, then the resistor stability is completely unimportant. If you hope to infer the current from a voltage measurement across the resistor, then you need stability and accuracy. How accurate? I reckon 5% is good enough when testing my batteries, YMMV.

Power Dissipation. If your dummy load should be able to dissipate say 2W, then an alli-clad 10W resistor may be good by itself. If you want to burn 10W, then you will need to mount it on a suitable heatsink. If the heatsink is small, you may need a PC fan to keep its temperature down. Heatsinks have a C/W specification. If you are fishing one out of your junk box, then check online suppliers to find one that matches its dimensions and form and use those specs. Or bolt a resistor to it, and see how hot it gets as you turn the power up. I like to keep heatsinks to 60C or less, but that's very conservative. If you don't have a thermometer, then 60C is the temperature at which you can touch a dry surface firmly for a few seconds before deciding you need to take your hand away. Domestic radiators run up to 82C, which is the temperature at which no skin damage occurs with a few seconds contact with dry skin, though I don't know how to judge that manually. The spec for the resistor may say it can run much hotter. How hot you want to run it is up to you.

My battery load tester consists of 6 10 ohm resistors connected in series, on heatsink, with a 4mm socket at each junction. I can use that as a 60ohm load, or a 1.67 ohm load, and lots of values in between, selectable by moving leads about. Just a thought

Syntax Error asked - 'From its physical specifications, would this make a good dummy load?'

It depends what the specification for your dummy load is, and what you mean by stable. 'Battery testing' is one application, but 'other purposes' leaves rather a lot to the imagination.

Stability. Over time, and/or over temperature? Loading a battery with a fixed resistor will mean the load current varies as the voltage reduces. So I can already assume you are not testing at a precise load, just in a general ballpark. If you are measuring the battery current, then the resistor stability is completely unimportant. If you hope to infer the current from a voltage measurement across the resistor, then you need stability and accuracy. How accurate? I reckon 5% is good enough when testing my batteries, YMMV.

Power Dissipation. An alli housed resistor will only be able to dissipate its rated power when properly heatsinked. A 10W rated resistor will certainly drop 1 watt in fresh air, maybe 2W before it gets too hot. You acn either use small fan-blown heatsink, or a bigger naturally convecting one. Heatsinks have a C/W specification. If you are fishing one out of your junk box, then check online suppliers to find one that matches its dimensions and form and use those specs. Or just bolt a resistor to it, and see how hot it gets as you turn the power up. I like to keep heatsinks to 60C or less, but that's very conservative. If you don't have a thermometer, then 60C is the temperature at which you can touch a dry surface firmly for a few seconds before deciding you need to take your hand away. Domestic radiators run up to 82C, which is the temperature at which no skin damage occurs with a few seconds contact with dry skin, though I don't know how to judge that manually. The spec for the resistor may say it can run much hotter. How hot you want to run it is up to you.

My battery tester load consists of 6 off 10 ohm resistors connected in series, on heatsink, with a 4mm socket at each junction. I can use that as a 60ohm load, or a 1.67 ohm load, and lots of values in between, selectable by moving the leads about. And yes, they are alli-cased. The heatsink is too small to naturally convect away their full rated power, but I rarely use it to 100% rating. When I do, I put it in front of a fan.