Battery lifespan in a garage is decided by the daily temperature band of the exact spot the unit hangs in, so the siting check comes before the quote: which way that wall faces, how much direct sun and heat soak the enclosure will take, how much air moves past it, and what else the garage is used for. Sustained operation above roughly 25-30°C accelerates capacity loss and pushes internal resistance up, and a wall that spends summer afternoons in the high thirties will cost more battery life than the cycle count on the datasheet ever suggests. Placement belongs in the quote, next to the cable route, the isolation points and the Certificate of Compliance, because where a battery lives is not a finishing detail. It is the operating condition.
Stand in my garage at two in the afternoon in February and put your forearm on the plaster next to the roller door. The door has been in the sun since midday and the wall behind it is warm enough that you leave your hand there for two seconds, not five. Now walk to the inside wall on the south side, the one the neighbour's carport shades from about eleven, and you can rest your arm there comfortably. Same room. Same afternoon. Ten degrees apart, possibly more, and both walls are perfectly good candidates for the same battery. That gap is the entire argument.
Then look up. If there is no ceiling, or a ceiling with nothing above it, the space just under the roof sheeting runs hotter again, and hot air sits there because nothing pushes it out.
The garage is not one temperature
People talk about "the garage" as though it has one climate. It has a north-facing wall that bakes from mid-morning, a shaded wall that never sees direct sun, a slab that holds the day's heat and releases it until ten at night, and a roof void that behaves like an oven with the door shut. Bolted to one of those surfaces is a sealed steel box full of cells that generate their own heat when they charge and discharge. The enclosure is not in the ambient temperature of your suburb. It is in the temperature of the surface it is fixed to, plus whatever the sun adds to the box itself, plus whatever the cells add inside it.
That is why two identical houses in the same street can get very different service life out of identical equipment. Orientation, shading, whether the garage has a ceiling, whether the roller door is steel or timber, whether a tumble dryer or chest freezer compressor is humming two metres away, and whether the door is left open for airflow or closed all day. I have watched a temperature probe sit on a west-facing garage wall in the late afternoon and read a number that made the installer go quiet. The number is not the point. The point is that nobody knows it until somebody checks, and the checking is cheapest before anything is ordered.
What heat hides from you in summer
Here is the part that catches people out. A warm battery often looks better than a cool one. Heat lowers internal resistance, so on a hot afternoon the pack delivers closer to its rated capacity, the state of charge reads well, and a quick self-consumption check on a sunny day looks healthy. If your only measurement of battery health is what the app shows you in January, the hottest month is also the month your system flatters itself.
Underneath that, calendar ageing is running faster. Capacity fade and rising internal resistance accumulate quietly in the heat, and they do not reverse when the weather cools. What you find in the second winter is that the pack that carried the house through load-shedding the previous year now reaches the bottom of its usable window sooner. Nothing failed. Nothing tripped. It simply aged out of the years you thought you had paid for.
This is also where warranty arguments get difficult. The datasheet for your unit will state an operating temperature window and charge and discharge conditions, and a claim years later often turns into a question about whether the installation respected them. Keep the datasheet figure in hand rather than relying on a general rule of thumb, because those windows differ between units. What does not differ is that the siting decision is the evidence.
Cold trims the edges, heat takes the years
Winter is a different problem with a smaller bill. Cold raises internal resistance and trims usable capacity in the short term, so on a Highveld morning at four, when the lights go out, a cold pack sags more under load and the management system may hold back what it will let you draw. That is annoying and it is real, but the long-term damage from cold is usually smaller than the long-term damage from sustained heat. A cold garage in a cold town is not the enemy. A hot box in a hot town is.
Coastal humidity adds its own slow tax on terminals and enclosures, which is another reason the position has to be a considered one rather than the leftover corner nobody wanted.
Why this has to be settled in the quote
Installation position is not only a thermal question. It has to satisfy the electrical prerequisites a competent installer checks anyway: the route and length of the DC cable back to the inverter, working space around the unit, isolation points, separation from anything with a flame, access for maintenance and eventual replacement, and where the main distribution board actually sits. In a garage that also stores petrol, gas cylinders, paint thinners or a welding bay, the conversation changes shape entirely. The wiring code behind the Certificate of Compliance has views on what belongs where, and the person signing that document is the person who has to be comfortable with the spot.
Here is the gap that costs people money. The Certificate of Compliance you receive afterwards confirms the installation is safe and compliant. It says nothing about whether the wall was a good choice. Compliance and suitability are two different tests, and only one of them is inspected.
That is why I now treat placement as a quote-stage question. By the time the installer arrives with a drill and a box, the decision has already been made. If it was made badly, the cheapest correction is a different wall, and the most expensive is a new battery in year six.
What a good answer sounds like
When I ask where the battery is going, I want to hear the reasoning out loud. Which wall, which direction it faces, what shades it and when, whether the garage has a ceiling, how hot the wall gets in the late afternoon, what else runs in that garage, and how long the cable run is to the inverter. A good installer will walk the garage and stand in it at the worst time of day rather than glancing at it at nine in the morning.
What makes me cautious is a siting decision that arrives without a reason. "They always go there." A position chosen because the cable was shorter. A wall that was free. A roof void picked because it is out of sight, which is the hottest place in most houses. None of those answers are dishonest, and sometimes they are the right call anyway, but they tell me the temperature band was never part of the thinking.
The trade-offs I have learned to live with
The perfect spot rarely exists. The cool wall may be the far side of the house, which means a longer cable run and a volt drop conversation. The shaded spot may sit next to a door that gets bumped by a car. The garage may double as a workshop, which rules out the only wall with decent clearance. Sometimes the wall available is the warm one, and then the answer is a design discussion about airflow, mounting height and shading before anything is ordered, handled by the installer rather than improvised after the fact. If the only sensible position is a hot one, I would rather hear that admitted in the quote, with the trade-off spelled out, than discover it in a summer that quietly costs me two years.
So the question I ask on every quote now is short. Where exactly, and why there. The answer tells me whether someone is siting a battery in my garage or just installing one.
