Best car battery tester for UK home mechanics: I read the code with the V310 first
A search for the best car battery tester usually starts on a UK drive in the wet: the crank is slow, or the engine light came on with the hard start, and a home mechanic wants to know which part to buy. I'd split that into two jobs. One is the battery on the posts. The other is the code the car stored. The tool we sell for the second job is the V310, a handheld OBD2 code reader. I'd reach for it when I want that code, the freeze frame and the I/M readiness screen before I spend money on a battery.
In the hand it is 155 × 85 × 25 mm and about 200 g. The box is the reader and its 16-pin OBD-II lead. It runs from the car at DC 9–16 V, drawing about 80 mA.
The battery check people expect, and the screen this reader actually has
When someone asks for a car battery tester they usually want the battery itself: a resting voltage, and on a conductance tester an estimate of cranking ability against the figure on the case. A load tester pulls current for a few seconds. If I were stood there with a slow crank and a dark dashboard, that is the reading I would want before I bought another battery.
The V310 menu is Read Codes, Erase Codes, View Freeze Frame and I/M Readiness. VIN and DTC buttons sit on the unit. Live data can include engine speed, coolant temperature, vehicle speed and calculated load, and the menu can show that data as a curve. If I were stocking a toolbox for cold-cranking checks, I would keep a separate battery tester for the posts and use this reader when the engine light is part of the story.
A charging fault or a sensor fault can sit behind a hard start, and the stored engine code is what this screen can show. If the crank is slow and Read Codes comes back empty, I would still have the battery measured on its own.
How I use it from the driver's seat
Leave the car in park or neutral with the handbrake on. I do the reading from the seat, with the ignition on, lead plugged into the diagnostic socket. I stay out from under the car.
On a right-hand-drive car the 16-pin socket is usually within reach of that seat, often under the dash or behind a small cover. Plug the lead in, then turn the ignition on. Power comes from the port. If the port is outside the DC 9–16 V window, the reader has nothing to run on, and I stop there and sort the battery or the connection.
- Choose Read Codes. The DTC button puts the code meaning on the screen.
- Open View Freeze Frame for the snapshot stored with the code.
- Open I/M Readiness for the monitor status.
- Use the VIN button when you want the chassis number on the same unit.
The code and the freeze frame are there with the ignition on. Engine speed on the live screen moves once the engine is running. Coolant temperature, vehicle speed and calculated load are the other live values listed for this model. I treat the DTC line as the stored code and its on-screen wording. I would check that wording against this car before I ordered a part.
It suits cars with a 16-pin OBD-II port on the protocols listed for the V310: SAE J1850, ISO 9141-2, ISO 14230-4 KWP and ISO 15765-4 CAN. The baud list is on the V310 code reader page. If I were looking at a 24-volt lorry, I would leave the V310 in the car kit. The working voltage on the port is DC 9–16 V.
What I do before I clear anything
Write the code down and open the freeze frame before you touch Erase Codes. On this reader you clear a code after the fault is fixed. If the fault is still there, the light can come back.
On an OBD-II car, an erase usually clears that stored snapshot and puts the readiness monitors back to incomplete. They complete again after the car has run its own checks. That pattern belongs to the maker, so I would quote a mileage only when the handbook gives one. The I/M Readiness item is on the menu so you can see the status before and after.
For the MOT I follow the lamp check in the DVSA inspection manual, section 8. The tester turns the ignition on and checks that the engine malfunction indicator lamp lights, then goes out. On some cars the engine has to be started before it goes out. For ordinary petrol cars first used on or after 1 July 2003, and for diesels first used on or after 1 July 2008, an engine MIL that is inoperative or indicating a malfunction is a Major defect. I read the code and the freeze frame, get the fault fixed, and erase after that. I would leave the lamp showing on the morning of the test if the fault is still in the car.
The AA's engine-light note treats a steady amber light as a reason to finish the trip gently and get the car checked, and a flashing or red light as a reason to stop when it is safe. I would take the code reading first, then follow that. Storage for the reader is -30°C to 65°C, which covers a UK garage shelf. Unplug the lead once you have the reading. While it is powered from the port the working current is about 80 mA.
When I would put the reader down
If the light is flashing, or the car is down on power and misfiring, I would stop when it is safe and get the car looked at. A code on the screen is useful while you are still in the seat. It is a poor reason to keep driving.
If I were buying a tool for an ABS, airbag or gearbox warning light, I would leave the V310 on the shelf. The menu is engine codes, freeze frame, I/M readiness, vehicle information, the VIN and those live engine values. That is the job I would trust it with.
The reader, the menu and the price are on our V310 code reader page.