SOC, reserve %, and when to search for chargers

This is the floor you never want to cross on arrival at a charger. Highway surprises — traffic, AC load, a missed exit — eat margin. Keep 20% unless you know the leg well.

When your estimated SOC along the route hits this level, the planner looks for DC stops. Lower threshold = later stops (riskier). Higher = earlier stops (safer, more time charging).

Brochure range is optimistic. Enter your average Wh/km from past drives — presets pre-fill for Nexon, Punch, etc. — so arrival % on each stop card is trustworthy.

Suppose a 45 kWh pack and 165 Wh/km. Usable energy at 90% start with 20% reserve is 0.7 × 45 = 31.5 kWh, about 190 km of highway before you must be at a charger. Search threshold at 30% means EV Grids starts looking earlier than the floor — that gap is the closed-site buffer. If you set both to 10% to ‘skip a stop’, you have donated your margin to hope.

Raise reserve on ghats, monsoon, and when the next charger is a single gun. Lowering search threshold to 22% with reserve at 20% is almost the same as having no search margin. Keep at least 8–10 points between them.

The chart on EV Grids is a sketch along the Google polyline using your inputs. It is not your BMS, not a live telemetry stream, and not a promise if you then drive 115 km/h in 42°C. Believe the lower of the two numbers: the card and the dashboard.

Reserve is the floor you will not cross. Search threshold is when you start looking. The distance between them is your entire margin for error — traffic, a missed exit, a detour around roadworks, or a charger that turns out to be inside a gated complex.

Setting them close together, say 25% reserve and a 28% threshold, means the planner starts hunting when you have almost no room to be choosy. A wider gap costs you a slightly earlier stop and buys the ability to reject a bad site and continue to a better one.

Raise both for ghats, monsoon nights, sparse stretches, and unfamiliar roads. A 25–30% reserve on a Western Ghats descent is not timidity: regenerative braking may return less than you expect, and the nearest alternative can be an hour away.

Lower them only on corridors you know, where you have alternatives in sight and you are confident in your consumption figure. Never lower reserve to make an itinerary look cleaner — that is optimising the screen instead of the drive.

Suppose a 45 kWh usable pack, 165 Wh/km on the highway, start SOC 90%, reserve 20%, search threshold 30%. Spendable energy is 70% of 45 kWh — about 31.5 kWh — which is roughly 190 km before you would hit the reserve floor at that consumption. The planner starts looking for DC when the walk hits 30%, so the first search happens earlier than 190 km. That gap is the point of two numbers instead of one.

If you drop reserve to 10% to ‘make it’, you have converted a planning tool into a dare. A missed exit, a closed plaza, or 15 minutes of 40°C traffic with HVAC on will eat that 10%. Keep 20% until you know the leg, then maybe 15% on a dense NH48 Tuesday — not on NH66 in July.

Search threshold below reserve is a configuration error: the planner would try to arrive below the floor you said you would not cross. Keep threshold at least 8–10 points above reserve. New highway drivers often run 30/20; monsoon and ghats 35–40 / 25.

ARAI or WLTP kilometres assume a cycle you will not drive. Highway 100 km/h, HVAC, and a 1–2% grade change the Wh/km. EV Grids walks energy along the driving polyline using your Wh/km (or the preset). Rated range is only used to imply pack energy when the preset has no kWh field. Mixing the two — ‘I have 400 km range so this 380 km road is one shot’ — is how people arrive at 8%.

After two or three real trips, replace the preset Wh/km with the car’s trip computer average for similar roads. Then the arrival % on each stop card starts to look like your dashboard instead of a hope. The SOC chart is still a sketch. The car wins arguments.

Start with the EV Grids preset reserve (often 20%) and a search threshold about ten points higher. That pairing is for a first NH44 or NH48 day when you have not yet logged Wh/km. After two similar trips, you may drop reserve to 15% on a dense Tuesday with multi-gun plazas in the next town. Do not copy a 10% reserve from a YouTube run that started at 100% in January.

Monsoon, ghats, and 40°C HVAC are the three reasons to raise both numbers together. A 35% search / 25% reserve pair on NH66 in July is not timid; it is how you still have a second site in range when the first listing is a flooded approach road. Enable hills and weather in the planner on those days so the SOC walk is not a dry-season walk.

If the stop card shows arrival near reserve, you did not ‘save a stop’. You spent the backup. Recalculate with a higher start SOC, a lower cruise Wh/km (slower), or an extra via-point charger. The threshold and reserve sliders exist so the API searches earlier, not so you argue with the chart at 12%.